Mirroring object on Z axis not correct
So what you're doing here is using your hammer object (called Cube) as Mirror Object. The problem is that the origin of Cube is not place at the center of its geometry, so the mirrored mesh will be a bit shifted. To fix that, in Edit mode select the top and bottom vertices of Cube and press ShiftS &gt; Cursor to Selected, then back into Object mode, right click &gt; Set Origin &gt; Origin to 3D Cursor. Now the ornment will stick to the surface.